1. Field of the Invention
The present invention relates to an optical correlator utilized for photometry, optical information processing and the like. More particularly, the present invention relates to an optical correlator which identifies a target object automatically from among two-dimensional images through a coherent optical correlation process.
2. Description of the Prior Art
Various types of optical correlators are known.
One type of optical correlator utilizes a method for making a correlation filter by means of holography for detecting correlation. However, the method requires holograms which make use of Fourier transform patterns for comparison of specifically prepared images which is time consuming and since a pertinent space modulator is not provided for the holograms of the prior art, the holography utilizes a method for recording images lacking in real time efficiency.
Therefore, K. Kasahara, Japanese Patent Laid-Open Nos. 138616/1982, 210316/1982, 21716/1982, discloses an optical correlator utilizing a method for transforming two coherent images into first Fourier transform images through a Fourier transform lens, transforming first Fourier transform images into second Fourier transform images through a Fourier transform lens again, and generating a self-correlation peak and a cross-correlation. The optical correlator is realized with a quasi-real time operation by using a liquid crystal display device for forming two pictorial information sets for comparison with one another however, the two compared images or sets must be spaced apart substantially, thus the operation requires a large optical system or resolution decreases. Further, in case one of the two compared images moves relative to the other, the prior art optical correlation has an extremely narrow field of view and is not operable for minute positioning.